Magnesium base alloys



Patented July 22, 1952 chester, England, assignor to Magnesium ElektronLimited, Manchester, England, a British omp any No Drawing. ApplicationOctober 8, 1949, Serial N 0. 120,422. In Great Britain July 4, 1949 1 J.This invention relates to the production of magnesium-base alloys, andin particular to the introduction of one or more of the'rare earthmetals into the alloy in quantities not exceeding 15 per cent andusually from 1 to 8 per cent.v For thispurpose, it is possible toobtainrare earth metals in metallic form which, however, are

usually contaminated with appreciable quantities of iron and silicon.These impurities are, however, deleterious when introduced intomagnesium alloys, especially magnesiumalloys containing zirconium. It isfound that even comparatively smallproportions of iron and silicon willmilitate to a considerable extent against the introduction of zirconiuminto the magnesium. I have, therefore, considered the possibility ofintroducing rare earth metals by means of reducible salts of thesemetals.

It has. been suggested in British Patent No. 342,586 to incorporatecerium chloride in-fluxes to be used with alloys containing rare earthmetals, these fluxes containing magnesium chloride, and the object ofthe cerium chloride being to give rise to sufiicient cerium on reactionwith the magnesium to offset the cerium loss which would otherwise becaused by reaction with the magnesium chloride. I have performed anumber of alloying experiments with cerium chloride but this substanceis deliquescent, volatile, readily hydrolysed and expensive, and is,therefore, not well adapted to serve as a commercial source for theintroduction of cerium. Moreover, reduction of the cerium chloride bymagnesium is far from complete. These remarks are also applicable to thechlorides of other rare earth metals.

I have, therefore, carried out experiments with a view to using thefluorides of the rare earth metals for alloying purposes. Thesefluorides are however highmelting pointsolids, and it therefore appearedto me desirable to search for some suitable solvent to assist in thereduction at temperatures suitable for treatment of magnesium.Experiments showed thatthe rare earth metal fluorides were insoluble inalkali metal chlorides and also in alkaline earth metal chlorides withwhich they did not react. I

therefore tried various low melting mixtures of It was found thatvarious fluoride mix- 2 Claims. (01. 75-67) Considering the possible useof potassium fluoride, I discovered that potassium fluoride formed a lowmelting point mixture with rare earth fluorides if the proportions ofthe substances were kept within certain limits, and if sufiicientpotassium chloride was added to prevent the mixture from reactingviolently with magnesium, the resulting composition could be used forintroducing rare, earth metals into magnesium. Itwas also found that therare earth metal alloying efliciencies using such compositions weresuperior to those that obtained with rare earth chlorides.

I have considered the possibility of using sodium fluoride in place ofpotassium fluoride, and of using sodium chloride, calciumchloride,strontium chloride or magnesiumchloride in place of potassium chloridewith a view to effecting further improvements in alloying efliciency.The use of'sodium fluoride results however in the incorporation into thefinal alloy of undesirably large amounts of sodium, which in all casesproduces a marked increasein the tendency of the alloys to burn duringcasting, and inthe case of alloys containing zirconium exercises adeleterious effect on tensile properties, particularly in the sand caststate. The alloying composition should not contain more than 5 per centsodium fluoride if any. Substitution of sodium chloride for thepotassium chloride also gives rise to somewhat increased sodium contentsin the final alloys. On substituting calcium chloride, strontiumchloride and barium chloride for the potassium chloride, it is foundthat a reaction occurs in which the potassium fluoride is converted topotassium chloride 'With subsequent precipitation from solution of therare earth fluoride, and deterioration in the alloying efliciency. Itappears therefore that the most satisfactory chloride to use in order toprevent the mixture of rare earth fluoride and potassium fluoride fromreacting violently with the magnesium during alloying is'potassiumchloride.

According to the present invention therefore, an alloying composition'for introducing rare earth metals into magnesium consists of thefluoride of the rare earth metaLsufiicient potassium fluoride todissolve the rare earth metal fluoride at the alloyingtemperature (e. g.700 C. to 850 C.) and at least asufficient quantity of an alkali metalchloride to prevent violent reaction, other of the aforementionedchlorides, if any, not exceeding 5 per cent. In particular, magnesiumchloride should be absent. a I

Whilst the minimum quantity of potassium fluoride is that required todissolve the rare earth metal fluoride, a somewhatgreater proportion maybe used in order to produce greater fluidityat the alloying temperature,and a corresponding 3 increase in the proportion of the alkali metalchloride is then used. The quantity of potassium fluoride is preferablyat least an equimolecular proportion in relation to the rare earth metalfluoride. The proportion of alkali metal chloride should be at least onechemical equivalent of the potassium fluoride. 1

The quantity of alkali metal chloride is preferably from 5 to per centof the total weight of I flux more than the quantity of potassiumfluoride and from to per cent less than the quantity of rare earth metalfluoride. The alkali metal chloride and potassium fluoride together arepreferably from 5 to 15 per cent less than the quantity of rare earthmetal fluoride.

. The ingredients of the-composition should fall 7 within the followinglimits:

For example, a mixture consisting of 55% rare earth metal fluoride, 17%potassium fluoride and 28% alkali metal chloride gives satisfactoryresults. 1 In practice, I prefer to use potassium chloride as the alkalimetal chloride.

Certain ingredients otherthan those hereinbefore mentioned may beincorporated into the composition viz:

1. One or more rare earth metal chlorides or oxides preferably notexceeding 10 per cent each andnot exceeding 15 per cent in total. Theseshould however preferably not exceed 4 per cent.

2. Up to 5 per cent of one or more oxides inert to magnesium and'whichdo'not react with rare earth metal chlorides e. g. MgO (preferably notmore than 2 per cent).

3. Up to 5 per cent of one or more fluorides of alkaline earth metalsincluding magnesium. The total of these fluorides and the oxidesmentioned under 2 should not exceed 5 per cent (preferably however notexceeding 2 per cent).

4. Up to 10 per cent (preferably not more than 5 per cent) of bromidesof alkali metal and alkaline earth metals.

5; Some lithium chloride and/or bromide, e. g. up to 10 per cent(preferably less than 5%) The total proportion in the alloyingcomposition of rare earth metal fluorides, potassium fluoride and alkalimetal chlorides, should be at least,80 :per cent and preferably at least95 per cent;

In the production of magnesium base alloys containing for example about3 per cent. rare earth metals, the following procedure may be adopted.The magnesium or magnesium alloy to be melted is charged to the'crucibleand a quantity of the composition equal to about 12 percent of theweight of metal also added. When melting is complete, the temperature ofthe metal is raisedto about 830 C., and the metalis'puddled for 10 to 15minutes using an alloying tool consisting of a perforated plate with ahandle attached at right angles. During the puddling process, it isdesirable to use a flux which does not contain magnesium chloride, e. g.the flux described in the specification of British Patent No. 652,235.

In addition to the method described, the composition may be contactedwith the magnesium or magnesium alloy in other ways, e. g., thecomposition may be added in the form of lumps or powder to the melt whenthe metal is molten, or the metal may be poured on to the composition,the latter being either in the solid or molten state. Mechanicalstirring'may be substituted for puddling by hand.

When preparing alloys containing both ziricomum and rare earth metals,the addition of i the zirconium can be'made before or after theintroduction of the rare earth metal or may be simultaneous therewith.For introduction of the zirconium, the alloying composition of U. S.Patent 2,452,914 may conveniently be used, and this can be chargedto thecrucible with the metal to be melted or may be contacted with the moltenalloyv in other ways, e. g., by stirring the alloying composition eitherin the form of lump or powder into the molten metal, or the metal may bepoured on to the composition, the latter being in either the solid orliquid state. Mechanical stirring may be used. j

In remelting ingot or scrap alloy containing rare earth metals it isdesirable to introduce a further quantity of the alloying compositioninto the crucible and conveniently this'isadded to the crucible beforeor at the same time as the scrap. It can however be added at a laterstage. The Weight of alloying composition required in remelting alloycontaining 3 per cent of rare earth metals will for example be from oneto two per cent of that of the alloy, and its use will enable the rareearth metal content of the final alloy to be closely controlled.

In the production'of magnesium base alloys containing zirconium as wellas rare earth metals, the zirconiurn alloying substance may beintroduced into the molten magnesium at the same time as or afterintroducing the rare earth metal alloying composition.

I claim.

1. A composition of the character described, for use in producingmagnesium base alloys, consisting of 45 to of at least one rare earthmetal fluoride, 12 to 25% of potassium fluoride and 20 to 40% of atleast one alkali metal chloride.

'2. A composition for use in producing magnesium base alloys consistingof from 80 to 98% of a main component and from. 20 to 2% of a subsidiarycomponent, the main component consisting of: rare earth metal fluorides45 to 65% by weight of the component, potassium fluoride 12 to 25% byweight of the component and alkali metal chloride 20 to 40% by weight ofthe com- .ponent, the subsidiary component consisting of at least one ofthe following: 0 to 5% of sodium chloride, 0 to 5% of an alkaline earthmetal chloride, 0 to 10% of a chloride of a rare earth metal, 0 to 10%of an oxide of a rare earth metal, 0 to 5% of an oxide inert tomagnesiumyO to 5% of anoxide inert to rare earth metals, 0 to 5% of a'fluoride of an alkaline earth metal, 0 to 10% of a bromide of an alkalimetal, 0 to 10% ofa' bromide of an alkaline earth metal, EDWARD F.EMLEY.

REFERENCES orrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name 1 Date 2,250,687 Von Zeppelin July 29,1941 2,251,088 Von Zeppelin July 29, 1941' 2,452,914 Emley i Nov. 2,1948

1. A COMPOSITION OF THE CHARACTER DESCRIBED FOR USE IN PRODUCINGMAGNESIUM BASE ALLOYS, CONSISTING OF: 45 TO 65% OF AT LEAST ONE RAREEARTH METAL FLUORIDE, 12 TO 25% OF POTASSIUM FLUORIDE AND 20 TO 40% OFAT LEAST ONE ALKALI METAL CHLORIDE.